<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div class="box">盒子</div>
    <div class="box">盒子</div>
    <div id = 'nav'>
        <ul>
            <li>首页</li>
            <li>产品</li>
        </ul>
    </div>
    <script>
        // 1.getElementsByClassName
        var boxs = document.getElementsByClassName('box');
        console.log(boxs);
        // 2.querySelector 返回指定选择器的第一个元素对象 切记里面的选择器要加符号
        var firstbox = document.querySelector('.box');
        console.log(firstbox);
        var nav = document.querySelector('#nav');
        console.log('nav');
        var li = document.querySelector('li');
        console.log(li);
        // 3.querySelectorAll()返回所有对象集合
        var allBox = document.querySelectorAll('.box');
        console.log(allBox);
        var lis = document.querySelectorAll('li');
        console.log(lis);

    </script>
</body>
</html>